To be suitable for use in harsh environments, such as space or manufacturing, electronics must be particularly robust, reliable, and have a reduced susceptibility to electromagnetic interference, while at the same time providing a satisfactory rate of data throughput for the application. Additionally, it may be desirable to galvanically isolate electronic components from one another in such environments, so as enhance operational stability of the components by reducing the likelihood that operational parameters or malfunction of one component will interfere with the functioning of another. As is known in the art, “galvanic isolation” between electronic components means that although information may pass between the components, charge-carrying particles do not. Galvanic isolation is particularly useful in situations where the electronic components have different ground potentials, because transfer of charge-carrying particles from one component to another may change the ground potential of one or both components, thus disturbing the operation of one or both components.
For example, electronic components on spacecraft, e.g., space vehicles and satellites, may be configured so as to comply with the SpaceWire (ECSS-E-ST-50-12C) and/or SpaceFibre standards. The SpaceWire and SpaceFibre standards are both incorporated by reference in their entireties herein. SpaceWire is a standard developed by the European Space Agency (ESA) intended to ease the interconnection of various electronic components in spacecraft, and provides for data rates between 2 and 200 Mbits/second. SpaceFibre is an extension of SpaceWire that is also being developed by the ESA, and provides for even higher data rates, e.g., of up to 6 Gbits/second or higher. Neither standard requires that electronic components be galvanically isolated from one another, although both standards permit galvanic isolation. Instead, the SpaceWire and SpaceFibre standards define a physical layer in which low voltage differential signaling (LVDS) techniques use copper media to transmit signals from one line replaceable unit (LRU) on the spacecraft to another. Each LRU may implement physical schemes that are configured to provide LVDS signaling interconnectivity with another LRU, and an electronic element such as a field-programmable gate array (FPGA) that is configured to provide one or more functionalities implementing signal conditioning compatible with SpaceWire and/or SpaceFibre signaling standards, as well as other data generating functions supporting an imager or a sensor. The SpaceWire and SpaceFibre standards require the LVDS signaling scheme between the LRUs comply with the ANSI/TIA/EIA-644 standard, the entire contents of which are incorporated by reference. The LVDS signaling protocol implements differential signaling techniques including that the balanced differential lines have tightly coupled equal but polar opposite signals which reduce EMI. Specifically, at some lower data rate implementations, the magnetic fields radiated by each of the lines are drawn toward each other, causing cancellation of much of the magnetic fields. [AN-5017 LVDS Fundamentals, Fairchild Semiconductor, June 2005]. While single ended, galvanically isolated, interconnects are also attractive, many applications choose to use LVDS which require a pair of differential signals, i.e., a positive going signal and a negative going signal which are inverse mirror images, to gain signal integrity.
However, merely coupling the LRUs with metallic cabling or other non-isolating interface conforming to the LVDS signaling protocol may not sufficiently isolate the LRUs from one another. As such, if the LRUs operate at different grounds from one another, charge-carrying particles may move from one LRU to another via the interface, modifying one or both grounds and thus potentially disrupting proper functioning of one or both LRUs. Or, for example, power supply failure of one of the LRUs may propagate to the other LRU via the interface, which may cause over-voltage emission. Or, for example, immersion of the spacecraft within a plasma while in orbit may cause voltage buildup internally and/or externally, which buildup may discharge to an LRU and propagate via the interface to another LRU, disrupting the operation of both LRUs. Or, for example, electrical transients induced by lightning in electrical circuits due to coupling of electrical fields, e.g., for launcher applications, also may propagate from one LRU to another, disrupting the operation of both LRUs. Furthermore, within a given LRU, any non-galvanic coupling between the internal components of that LRU may render each of the components susceptible to similar disruption.
Some methods that have been considered for mitigating the effects of electromagnetic interference (EMI) in spacecraft include providing a controlled grounding scheme throughout the spacecraft, as well as controlling the local ground level in printed circuit boards (PCBs) and in LRUs. Additionally, it has been considered to use power converters with over voltage protection, so that if a power supply of one LRU fails, the failure does not propagate to a connected LRU. Or, for example, the spacecraft itself may be designed as a “Faraday cage,” may have surfaces designed to inhibit or control electrical discharge, may have enclosed electronic boxes, and/or may use shielded cables as well as over-shielding on cable bundles. Nonetheless, despite such safeguards, any non-galvanically isolated coupling between electronic components of the spacecraft, e.g., direct coupling between or within LRUs, may allow the transfer of charged particles from one component to another, thus potentially disrupting operation.
Although galvanic isolation interfaces have been known for some time, previously developed galvanic isolation interfaces may have reduced reliability in harsh environments, may have relatively limited data throughput rates, and/or may be incompatible with SpaceWire or SpaceFibre standards. For example, it has been proposed to use transformer-based or capacitance-based galvanic isolators, or opto-couplers, with SpaceWire links. However, the data throughput rate provided by transformer-based galvanic isolation may be insufficient to meet SpaceWire and/or SpaceFibre standards. Capacitance-based galvanic isolators may support sufficient data throughput rates, but may have reduced reliability if exposed to high electromagnetic interference. Opto-couplers may also support sufficiently high data throughput rates, but may degrade over time and may be susceptible to radiation.
U.S. Pat. No. 8,064,872 to Dupuis discloses an integrated circuit having radiofrequency (RF) isolation circuitry located in metal layers on a silicon substrate. The usefulness of such an integrated circuit in a spacecraft may be limited by eddy currents that may develop in the silicon substrate if the circuit is exposed to electromagnetic interference such as may arise in orbit.
U.S. Pat. No. 5,105,171 to Wen et al. discloses a coplanar waveguide directional coupler formed on a surface of a substrate and/or a microwave monolithic integrated circuit (MMIC) chip that is flip-chip mounted on the substrate and coupled thereto by conductive bumps. Wen discloses that the coupler may be used as part of a Doppler radar transceiver. Wen is silent on configuring the coupler so as to make it suitable for use in interconnecting spacecraft electronic components in a galvanically isolated manner.
U.S. Pat. No. 6,895,224 to Munday et al. discloses a low noise amplifier (LNA) that includes a Lange coupler that receives a signal and splits the signal into two symmetric signals that are then fed into a separate amplification section of the LNA. Munday is silent on configuring the LNA so as to make it suitable for use in interconnecting spacecraft electronic components in a galvanically isolated manner.
Accordingly, there is a need to provide a galvanic isolation interface solution suitable for use in providing signals between electronic components on a spacecraft especially for implementing high data rates needed for applications/functionality within LRUs.